Hard disk drive incorporating rotating magnetic disks is commonly used for storing data in the magnetic media formed on the disk surfaces, and a movable slider including read sensors are generally used to read data from tracks on the disk surfaces.
Presently, magnetoresistive (MR) read sensor, commonly referred to as MR sensor, is the prevailing read sensor because of its better capability to read data from a surface of a disk at greater track and linear densities than thin film inductive heads. An MR sensor detects a magnetic field through the change in the resistance of its MR sensing layer (also referred to as an “MR element”) as a function of the strength and direction of the magnetic flux being sensed by the MR layer.
Now, several types of MR sensors have been widely used by disk drive manufacturers in succession. One is anisotropic magnetoresistive (AMR) sensor, which makes the angle between the magnetization direction and the direction of sense current flowing through the MR element change and, in turn, cause a change the resistance of the MR element and a corresponding change in the sensed current or voltage. Another type is giant magnetoresistive (GMR) sensor manifesting the GMR effect. The GMR effect is a phenomenon that the magnetoresistive ratio (MRR) will change under an external time-changing magnetic field. The GMR sensor includes two ferromagnetic layers and a non-ferromagnetic layer sandwiched between the two ferromagnetic layers. The resistance of the non-ferromagnetic layers varies with the magnetic moments of the ferromagnetic layers, the conduction electrons and the spin-dependent scattering. Still another type of MR sensor is tunnel magnetoresistive (TMR) sensor, which includes a magnetic tunnel junction (MTJ) where the tunneling magneto-resistance effect (TMR effect) occurs. The TMR sensor has become the mainstream MR sensor due to its more remarkable change of MRR by replacing AMR sensor and GMR sensor.
However, high temperature noise (HTN) problems always exist in the above-mentioned MR sensors and influence their working performance seriously. As well known, higher bias current/bias voltage is needed to provide better performance of the MR sensor, but higher bias current/bias voltage applied will bring higher temperature rise, in turn, induce high temperature noise. Thus, it is necessary to seek a balance between the temperature and the bias current/bias voltage according to the correlation between the temperature and the bias current/bias voltage.
To solve above difficult problem, for a GMR sensor, a method for measuring the temperature rise induced by bias current/bias voltage is performed. Since the whole GMR sensor is made of metal, the temperature rise can be estimated by using conductor's method. However, the TMR sensor does not belong to conductor, above-mentioned conductor's method can not be implemented for a TMR sensor so as to measuring the temperature rise in its magnetic tunnel junction (MTJ).
Hence, it is desired to provide a method for measuring the temperature rise induced by bias current/bias voltage in a magnetic tunnel junction (MTJ).